Daido Tokushuko Kabushiki Kaisha

Kazushige Kitou

Takao Shimizu

Hirotsugu Horio

Shigeyuki Inagaki

Ryuzo Yamada

Carbon steel pipes are joined to each other in a non-oxidizing atmosphere by using an insert constituted by a Ni-base alloy or a Fe-base alloy having a melting point which is lower than 1200&deg; C. and a thickness of 80 mm or smaller under conditions that the surface roughness Rmax of the joined surfaces of the carbon steel pipes is 20 &mgr;m or smaller, the joining temperature is not lower than 1250&deg; C. nor higher than 1330&deg; C., duration at the joining temperature is 30 seconds or longer and the pressure is not lower than 2 MPa nor higher than 4 MPa. The expanding operation is performed such that the maximum difference in level of the joined portion is not larger than 25% of the carbon steel pipe and the expansion ratio is 25% or lower.

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Nagoya, Japan

Kazushige Kitou